The Korean War catapulted Stanford University’s Electronics Research Laboratory (ERL) into a major player in electronic intelligence and electronic warfare systems. Encouraged by their Dean, Fred Terman, scientists and engineers left Stanford Electronics Research Laboratory to set up companies to build microwave tubes and systems for the military. Funded by military contracts these 1950’s startups would help build Silicon Valley’s entrepreneurial culture and environment.

The Beginnings – “Vacuum Tube Valley” Ecosystem circa 1950From its founding in 1946 Stanford’s Electronics Research Laboratory (ERL) did basic research into vacuum tubes that could operate at microwave frequencies. The research was funded and paid for by the Office of Naval Research (ONR) and later by the Air Force and Army. Much of the basic research work was done by advanced students or by recent Ph.Ds doing postdoctoral internships, supervised by Stanford engineering faculty members or senior research associates (staff.)

In a 1950 proposal to the Navy Fred Terman noted that the work that Stanford proposed “correlates almost ideally with related industrial activities in this area.” There were already “tube manufacturers in the area (Eitel-McCullough, Litton Industries, Varian Industries, Henitz and Kaufman and Lewis and Kaufman) that represented an integrated set of tube facilities for basic research, advanced development, engineering of new tubes, model shop and pilot and quantity production. And that circuit work is carried on by several organizations in the neighborhood, with Hewlett Packard Company being especially notable in this regard.” Terman was describing the valley’s already existing ecosystem for building vacuum tubes in 1950.

But unlike the majority of existing tube manufacturers in the valley who were making products for radios, Stanford Electronics Research Lab tube group had a special customer with very special needs – the U.S. Air Force and its Strategic Air Command.

So what exactly was the Electronics Research Lab designing? What were these microwave tubes? Why were they so important to the military? And what were these electronic intelligence and warfare systems used for?

Stanford Joins the Cold War – Microwave Power TubesStanford’s work in microwave power tubes would solve two of the Strategic Air Command’s most important cold war problems.

These 1940’s jammers (built by the wartime lab headed up by Terman and his team now at Stanford) had been built around tubes originally designed for radio applications, put out 5 watts of power. This miniscule amount of jamming power was acceptable because each WWII bomber flew in formation with hundreds of other planes, together attacking just a single target each day. The combined jamming power of all the bombers on a mission was enough to saturate and confuse German radar. But in a potentialcold war attack on the Soviet Union, our bombers were not going to fly in a massed formation to attack one target. Instead we would attack multiple targets in the Soviet Union at the same time. And while a few bombers would penetrate the periphery of the Soviet Union together, each plane — now able to carry more explosive power than all the bombs dropped in WWII — would approach its target individually. As a result of this change in strategy (and explosive capacity), each bomber had to supply enough jamming power to defend itself.

B-47 – primary Strategic Air Command Bomber in the 1950’s

As a result, to protect its bombers flying over the Soviet Union the U.S. Air Force needed power tubes that had hundreds of times more power than WWII devices.

The U.S. Air Force also needed improvements in frequency agility to protect its cold war bombers. Frequency agility can be best described by what happened over Germany in WWII. As the allies jammed Germany radar, the Germans tried to avoid the effect of jamming by changing the frequency on which their radars transmitted. This was possible since the jammers in U.S. planes’ could only transmit on a narrow band of frequencies (providing spot jamming) and could not be retuned in the air. To cover all the possible frequencies German radars might be operating on, allied technicians pretuned the jammers before each bomber raid so that each plane transmitted on a different frequency. The combined effect of hundreds of planes in the bomber stream was to cover a broader frequency range than one jammer could by itself. (This technique of covering a broad range of frequencies was known as barrage jamming.)

(A good Radar tutorial is here, on the Radar Range equation here and Electronic Warfare tutorial is here. The links will download PowerPoint presentations.)

But nuclear warfare over the Soviet Union in the 1950’s meant that a single bomber needed jammers that could cover multiple frequencies, and could be tuned instantaneously. Not only did the US need more more powerful microwave power tubes, the power tubes had to be frequency agile, (able to be tuned in the air to different frequencies) to jam the Soviet radars. (For example, the Soviet P-20 Token was an early warning radar our bombers would encounter. It transmitted on 5 different frequencies over a band 300mhz wide. To jam it, all five frequencies had to be jammed at the same time. Our WWII jammers couldn’t do the job.)

Terman’s Systems Engineering Research Lab at Stanford would develop microwavepower tubes thatoffered a solution to both challenges and would be a a game changer for electronic warfare at the time.

High Power, Instant Tuning – Stanford’s contributionStanford’s Electronics Research Laboratory first contribution to high power microwave tubes for airborne electronic warfare in the 1950’s was the Backward Wave Oscillator (BWO). Stanford engineers realized that this tube, which had been invented in France, could electronically tune through microwave frequencies while producing almost a 1,000 watts of power – (equivalent to the output of 200 jammers over Germany in WWII.) Perfecting this tube for use as an airborne jammer became one of the labs primary objectives.

This was a critical development to support the new tactics of single bombers penetrating the Soviet Union. Equipping a bomber with several jammers built around Backward Wave Oscillator could give it enough power to use barrage jamming against multiple radars and get it through to its target. Stanford gave its Backward Wave Oscillator design drawings to tube manufacturers throughout the U.S. By the 1960’s, the U.S. Air Force would ultimately equip its B-52 bombers with 6,000 jammers using these these oscillators.

The Rise of “Microwave Valley” Stanford Tube Spinouts
A technician in Stanford’s ERL tube shop, Ray Stewart, thought he could build these Backward Wave Oscillators commercially, and left to start Stewart Engineering in Scotts Valley near Santa Cruz. The company had more orders from the military than it could handle. (Stewart would sell his company to Watkins Johnson, one of the most financially successful of the Stanford microwave tube spinoffs. More about Watkins-Johnson in the next post.) Stewart joined a growing list of other microwave startups beginning to populate the valley.

One of the early microwave spinouts from Stanford was built around a microwave power tube called the Klystron, invented by Terman’s students Russell and Sigurd Varian and William Hansen. In 1948 the Varian brothers along with Stanford professors Edward Ginzton and Marvin Chodorow founded Varian Corporation in Palo Alto to produce klystrons for military applications. (Fred Terman and David Packard of HP joined Varian’s board.) While the Klystrons of the 1950’shad too narrow and bandwidth and were too large for airborne use, they could be scaled up to generate megawatts of power and were used to power the U.S. ground-based Ballistic Missile Early Warning System (BMEWS) radars (and the Stanford Linear Accelerator.)

Another of Terman’s students, Charles Litton, would start several Silicon Valley companies, and in the 1950’s Litton Industries would become the leader in pulse and continuous wave magnetrons used in jammers and missiles. Magnetrons were the first high power microwave device invented in WWII. Used in radars systems and missiles, magnetrons could producehundreds of watts of power.

More to ComeThese first microwave tubes were just the beginning of a flood of innovativeproducts for the military. The next Stanford tubes and systems would revolutionize the Electronic Intelligence aircraft that were circling (and flying over) the Soviet Union.